Retinal stimulator



g- 28, 1956 G. E. TASSICKER 2,760,483 RETINAL STIMULATOR Filed Oct. 20, 1954 INVENTOR BY GRAHAM EDWARD TASSICKER Aitgs.

RETINAL STllVlULATOR Graham Edward Tassicker, Surrey Hills, Victoria, Australia Applicafion October 20, 1954, Serial No. 463,507

Claims priority, application Australia October 29, 1953 8 Claims. (Cl. 1281) This invention relates to the provision of a retinal stimulator for use in certain conditions of blindness or partial blindness where the retina is partly or wholly inoperative.

Blindness often results from the failure of the retina to function in the normal way, one cause of such failure being a condition known as choroidal and retinal degeneration. in such a case, the back of the retina fails to receive its blood supply from the choroid, with the result that the rods and cones of the retina fail to excite the various cells and fibres by means of which impressions are transmitted to the brain in accordance with the light pattern falling on the eye.

The object of my invention is to provide an artificial retinal stimulator which will serve under certain conditions to overcome or partly overcome defects in or lack of operation of the retina.

According to my invention, I provide a retinal stimulator which is suitably shaped and adapted to be inserted surgically into the eye and is constructed of, or covered at least in part with, material or materials adapted to stimulate artificially the cells and fibres of the retina when light falls on the eye. The retinal stimulator in accordance with my invention is preferably inserted at the back of the retina between the retina and the choroid, or it may possibly be inserted between the choroid and sclera if the choroid and retina are surgically inseparable due to disease.

The effectiveness of my invention has been demonstrated in practice. In the only case which has been so far tried, the insertion of the retinal stimulator between the choroid and the sclera was successful in giving the patient appreciation of light and large objects where there was no previous sensation of vision. Although the patient did not obtain any appreciable definition, it is thought that the insertion of the stimulator in front of the choroid instead of at the back of the choroid will be instrumental in greatly increasing the definition obtainable.

To facilitate the further and more detailed description of a preferred form of my invention, reference will now be made to the accompanying drawings, in which:

Figure l is a sectional plan view through equator of a left eye showing the stimulator in the preferred position, and

Figure 2 is a perspective view of the stimulator taken from the direction of the arrow 2 in Figure 1.

As shown in the drawings, the retinal stimulator consists of a disc it of between 5 and mms. diameter or greater and /2 to 1 mm. thick, dished to conform to the curvature of the retina 11, i. e. 10.5 mm. radius, and with a stepped projecting lug 12 to enable it to be held in position with sutures 13. The retinal stimulator may comprise a supporting base made of tantalum, platinum, gold, or any other metal which is compatible with biological tissue. The Whole surface is coated with a thin layer of photo-sensitive material such as selenium which has been brought to its photo-active form. The selenium crystal size must be as small as possible, so that the individual crystal potentials developed under the action of the light image will have as high a degree of resolution as possible.

It is possible for the retinal stimulator to be constructed in various other ways; for example, it might be possible to use a photo-sensitive material which itself has suflicient mechanical strength to obviate the necessity for providing a separate base. However, it is thought that the provision of a separate base for the photo-sensitive coating would be more satisfactory in practice.

As shown in Figure 1, the disc 10 is preferably inserted in the eye between the retina 11 and the choroid 14 with the concave surface of the disc directed towards the lens 15 of the eye. The lug 12 passes through the choroid 1d and the sclera l6 and is attached to the outside of the latter by sutures 13. Alternatively, the disc 10 could be inserted into the eye between the choroid and sclera. Although this simplifies the surgical operation, the result is not as satisfactory in practice.

it is thought that the retinal stimulator in accordance with the invention operates as follows:

When light entering through the eye falls on the photosensitive layer of the retinal stimulator, change in potential is developed which causes change in ionization or ion migration in the various fluids in the adjacent cell structures and this results in stimulation of either the rods and cones, or if these are non-existent due to disease, the amacrine, bipolar, horizontal or ganglion cells.

All materials immersed in, or in contact with liquids assume a definite potential with respect to the liquid, this potential being related to the rate of ionic exchange. In the case of certain photo-active materials, the potential varies according to the brightness of the light illuminating the system, the change in potential being known as the Becquerel effect. Thus when the retinal stimulator is in position in the eye, and the eye is in darkness, the stimulator assumes a certain steady potential, hereinafter referred to as the resting potential, with respect to the surrounding tissue. On illumination, the front of the stimulator assumes a changed potential with respect to the back, and this change in potential results in the change in ionization or ion migration and consequent stimulation referred to above.

For best results, the resting potential in the dark may be critical, and this potential can be adjusted either by selecting a different photo-sensitive material for the coating, or by coating only the front surface of the stimulator with the photo-sensitive material and selecting an appropriate metal for the rear surface. It is possible also that the direction of potential change on illumination may be critical for best results, that is to say, a change in a positive direction between dark and light may be more effective than a change in a negative direction.

I claim:

1. A retinal stimulator comprising a plate dished to conform to the curvature of the retina and which is suitably shaped and adapted to be inserted surgically into the back of the eye with the concave face thereof directed towards the lens of the eye, the concave face of the plate being of such material that light falling on the said face will cause the stimulator to stimulate artificially the cells and fibres of the retina.

2. A retinal stimulator as claimed in claim 1 in which the material is photo-sensitive.

3. A retinal stimulator as claimed in claim 2 and an extension on said plate whereby the plate may be secured in position in the eye.

4. A retinal stimulator as claimed in claim 3, in which 0 both sides of the said plate are covered with photosensitive material.

5. A retinal stimulator as claimed in claim 3, in which the plate and the extension are entirely covered with photo-sensitive material.

6. A retinal stimulator comprising a disc which is dished to conform to the curvature of the retina and which is adapted to be inserted surgically into the eye with the concave face directed towards the lens of the eye, and a lug attached to the disc whereby the disc may be secured in position in the eye, the disc and the lug being coated on both sides with selenium which has been brought to its photo-active form.

7. A retinal stimulator comprising a disc which is dished to conform to the curvature of the retina and which is adapted to be inserted surgically into the eye with the concave face directed towards the lens of the eye, and an oif-set lug attached to the disc whereby the disc may be secured in position in the eye, the disc and the lug being coated on both sides with selenium which has been brought to its photo-active form.

8. A retinal stimulator comprising a plate made of metal selected from the group consisting of platinum and gold, the plate being dished to conform to the curvature of the retina and adapted to be inserted surgically into the eye with the concave face directed towards the lens of the eye, and an off-set lug attached to the plate whereby the plate may be secured in position in the eye, the plate and the lug being coated on both sides with selenium which has been brought to its photo-sensitive form.

References Cited in the file of this patent UNITED STATES PATENTS 1,837,364 Ives Dec. 22, 1931 2,128,103 Thomas Aug. 23, 1938 2,378,438 Saslaw June 19, 1945 

